The availability and low cost of ammonium nitrate (AN) have resulted in its widespread use in explosive formulations for commercial blasting. The simplest of these formulations is a mixture of AN and fuel oil (ANFO) in the ratio of approximately 94.5:5.5 by weight. Other formulations include a wide assortment of slurries and emulsions which have been developed to provide advantages over ANFO in handling, water resistance and improved performance.
The success of commercial AN formulations has attracted attention to the possible use of AN as a major ingredient in military explosives. For military applications, however, the developmental thrust has been directed primarily at ways of utilizing more effectively the energy available from explosives containing AN. Typically, AN formulations do not behave ideally in the explosive sense in that the energy release is not sufficiently prompt to yield theoretical possible detonation velocities and pressures. Development of methods to correct this deficiency has been an important part of military research and development efforts over the past several years.
One approach has been to form low-melting eutectics comprised of AN and one or more explosive fuels. Eutectics offer increased intimacy of the ingredients, low melting points near those normally used in munitions loading plants and melt-cast properties compatible with conventional military loading operations. Increased intimacy of the ingredients results in improved performance in some instances.
Typical of the eutectic composite formulations under evaluation at this time is one comprised of ethylenediamine dinitrate (EDD) and AN in the ratio 49:51 by weight, called EA, with a melting point of approximately 103.degree. C. When the AN portion is modified to contain a ratio of 85:15 AN/KNO.sub.3 by weight, the formulation is now called EAK. KNO.sub.3 has been added to phase stabilize AN over the temperature range from -65 degrees F. to 165 degrees F. Other modifications include an additional ingredient, such as nitroguanidine, which lowers the melting temperature still further, to approximately 98.degree. C., when present to the extent of 8% by weight of the composition (NEAK). Another composite formulation typical of AN based composite explosive is a 2:1 mole ratio of AN:ammonium 3,5-dinitro-1,2,4-triazolate.
Melt-cast loading operations typically involve large quantities of molten explosives. The hazards involved require that large distances separate accumulated quantities of explosives, and long dwell times at elevated temperatures are a matter of concern. Shrinkage with attendant cast defects is a troublesome problem, worsened by the elevated temperatures at which melt-cast formulations are delivered to the containers into which they are cast. The large temperature excursions required for cooling further complicate the process by permitting settling of solid additives with attendant density gradients, as well as long periods of time required for cooling before the castings can be moved. These problems pose serious limitations upon production rates.